A manually operable circuit breaker is known (DE-OS 36 42 719) in which the entire overcurrent tripping unit is inserted as a plug-in module into mating terminals on the base of the circuit breaker to produce a visible isolating gap. The overcurrent tripping unit is interlocked by means of a finger-grip knob on the circuit breaker such that the overcurrent tripping unit can only be removed when the circuit breaker is open. This known circuit breaker involves a special design. Since visible isolating gaps are neither necessary nor desirable in every case, the design of this known circuit breaker is relatively complex.
There is therefore a need for a circuit breaker which provides a visible isolating gap without the need to considerably alter the design of a conventional circuit breaker.